CN113068307A

CN113068307A - Circuit board anti-seepage plating method

Info

Publication number: CN113068307A
Application number: CN202110333820.2A
Authority: CN
Inventors: 陈红华; 谢斯文; 许昌焰; 刘艺琼
Original assignee: Fujian Fuqiang Precision Printed Circuit Board Co ltd
Current assignee: Fujian Fuqiang Precision Printed Circuit Board Co ltd
Priority date: 2021-03-29
Filing date: 2021-03-29
Publication date: 2021-07-02

Abstract

A circuit board anti-seepage plating method comprises the following steps of carrying out alkaline etching after a pattern plating step in the circuit board manufacturing process to expose resin in a base material, and then carrying out alkaline washing, wherein the alkaline washing is to soak the base material in a 3-5% NaOH solution for 3-5 minutes or spray the base material in a 3-5% NaOH solution for 1-2 minutes; then the solder mask step is carried out, and then the gold immersion step is carried out. Different from the prior art, the scheme can effectively remove the roughness of the prepreg by carrying out alkali washing after the copper layer is etched, so that copper particles on the prepreg are washed away, and the problem of diffusion plating caused by residual copper or palladium elements in the gold immersion step is solved.

Description

Circuit board anti-seepage plating method

Technical Field

The invention relates to a processing method of a circuit board, in particular to a processing method of a circuit board for preventing diffusion plating.

Background

The immersion nickel immersion gold plating is a very common phenomenon in the chemical immersion gold process, the immersion plating not only generates scrap, but also has the more serious problem that a part of the immersion plating generates micro short circuit, the current electrical test can not be tested by 100 percent, and a part of bad plates can flow to a client side, so that the potential quality hazard is great. At present, the general immersion gold plating is mostly caused by the imbalance or other abnormalities of the liquid medicine in the immersion gold process, and is generally improved by adjusting various parameters of immersion nickel and gold, such as adjusting the activation concentration, adjusting the activity of a nickel cylinder and the like, but the immersion gold plating cannot be improved by adjusting immersion nickel and gold, namely the immersion plating caused by copper foil or plate, and the improvement of various parameters of the immersion gold is not large.

Disclosure of Invention

Therefore, a new circuit board processing method needs to be provided, and the problem of nickel and gold immersion plating of the circuit board in the prior art is solved.

A circuit board anti-seepage plating method comprises the following steps of carrying out alkaline etching after a pattern plating step in the circuit board manufacturing process to expose resin in a base material, and then carrying out alkaline washing, wherein the alkaline washing is to soak the base material in a 3-5% NaOH solution for 3-5 minutes or spray the base material in a 3-5% NaOH solution for 1-2 minutes; then the solder mask step is carried out, and then the gold immersion step is carried out.

Specifically, the circuit board is a plate formed by pressing copper foil and a resin prepreg at high temperature.

Specifically, the alkaline etching includes the steps of:

removing the film: washing off a dry film on the circuit board by using NaOH solution;

etching: washing copper materials on the circuit board by using alkaline etching solution, wherein the etching solution comprises the component ammonia water;

stripping tin: and washing off the tin layer on the circuit board by using acid tin stripping water.

Specifically, the method comprises the following steps of cutting, drilling, copper deposition, plate plating, imaging, pattern plating and alkaline etching: stripping, etching, stripping tin, cleaning (3-5% NaOH), welding resistance and gold precipitation.

Different from the prior art, the scheme can effectively remove the roughness degree of the prepreg by carrying out alkali washing after the copper layer is etched, so that copper particles on the prepreg are washed away, and the problem of diffusion plating caused by residual copper or palladium elements in the gold immersion step is solved.

Drawings

FIG. 1 is an electron microscope image of the circuit board diffusion coating according to the embodiment;

FIG. 2 is a diagram illustrating the copper particle residue on the substrate of the circuit board according to the embodiment;

FIG. 3 is an electron microscope image of voids in the substrate and the residual palladium element according to an embodiment.

Detailed Description

To explain technical contents, structural features, and objects and effects of the technical solutions in detail, the following detailed description is given with reference to the accompanying drawings in conjunction with the embodiments.

In the existing circuit board manufacturing process, a copper foil and a semi-cured resin sheet are subjected to high-temperature pressing, one surface of the copper foil, which is bonded with the semi-cured resin sheet, is a rough surface, and the rough surface has a certain roughness for increasing a bonding surface with the semi-cured resin sheet, or the bonding surface has a certain staggered copper tooth length, which is shown in fig. 1. The different roughness or copper tooth length when pressed with prepreg will have several adverse effects: firstly, the copper particles are trapped in the prepreg due to overlong length of part of copper teeth or other reasons, and the copper particles trapped in the prepreg cannot be removed by liquid medicine during etching, which is shown in the attached drawing 2. And the copper particles can be deposited with a nickel layer on the base material to generate diffusion plating when nickel and gold are deposited, secondly, the copper particles are sunk into the prepreg when the length of part of copper teeth is too long or other reasons, cellular cavities can be generated even if the copper particles are removed by the liquid medicine during etching (see figure 3), and the holes can remain palladium and cannot be cleaned during the nickel and gold depositing step to cause diffusion plating.

In order to overcome the problems, through repeated verification and batch test for many times, the problem of diffusion plating caused by abnormal materials can be solved through alkaline washing after etching, and the principle is as follows: the circuit board is mainly composed of copper foil, resin and glass cloth, the base material is exposed after the alkaline etching step, the resin in the base material can be bitten by alkali, and the alkaline washing has two functions: firstly, the alkali can slightly bite the resin of the base material to remove copper particles trapped in the prepreg, secondly, the resin which can slightly bite the base material can level part of larger honeycomb-shaped cavities to be convenient for cleaning, and reduce the liquid medicine residue of the subsequent procedures, especially the residue of the palladium liquid medicine of the nickel-gold precipitation procedure, the alkali cleaning of the method uses 3-5% NaOH, and the base material is soaked for 3-5 minutes or sprayed for 1-2 minutes after etching. NaOH is a common material in circuit board production and is easy to obtain. The method is simple and practical, and needs to be noticed that the method can only be cleaned after line etching and cannot be cleaned after resistance welding, because the resistance welding also contains resin, NaOH can bite and resist the welding to cause side corrosion of the edge of the welding pad, and the binding force of the printing ink is influenced. Therefore, the anti-seepage plating scheme comprises the following steps: cutting, drilling, copper deposition, plate plating, imaging, pattern plating, alkaline etching (including stripping, etching and tin stripping), cleaning (3-5% NaOH), solder resistance and gold deposition.

In a specific embodiment, a method for plating a circuit board with an impermeable layer is described below, which includes the following steps, after the step of plating a pattern in the circuit board manufacturing process (the steps before and after the step of plating are the same as those in the prior art), performing alkaline etching to expose the resin in the substrate, where in a specific embodiment, the alkaline etching includes the steps of:

Then carrying out alkali washing, wherein the alkali washing is specifically carried out by soaking for 3-5 minutes by using a 3-5% NaOH solution or spraying for 1-2 minutes by using a 3-5% NaOH solution; then the solder mask step is carried out, and then the gold immersion step is carried out. The scheme is suitable for processing the circuit board which is a board formed by pressing copper foil and resin prepreg at high temperature. In the absence of the alkaline washing step, the NaOH solution was used only in the film stripping step, and at this time, the etching solution was not applied to the copper layer, and the underlying base material layer was not exposed, and the effect of cleaning the base material was not exhibited. The alkaline etching solution in the etching step is the alkaline etching solution of which the main component is ammonia water, and the alkaline etching solution does not react with the base material, so that the effect of cleaning the base material cannot be achieved, and the same effect cannot be achieved by the nitric acid type tin stripping solution adopted in the tin stripping process. Therefore, when the alkaline cleaning process is not available, the step of depositing nickel and gold is directly carried out, palladium elements in the gold deposition solution can be remained in gaps, or copper particles are remained in the base material, and the technical index requirements cannot be met, and the related experimental data are as follows:

number of elements	Symbol of element	Element name	Atomic concentration	Mass concentration
					6	C	Carbon	75.89	57.14
8	O	Oxygen	18.81	18.86
					35	Br	Bromine	2.78	13.94
29	Cu	Copper	2.52	10.05

After finding the problem of diffusion plating, technicians mix gold precipitation liquid medicines with different components for multiple times, and after multiple tests and sampling researches of various links, the problem is found to be solved by adding an alkali washing step. Finally, the processing method for preventing the circuit board from being plated by the diffusion plating is developed, and the problem of the diffusion plating is solved.

It should be noted that, although the above embodiments have been described herein, the invention is not limited thereto. Therefore, based on the innovative concepts of the present invention, the technical solutions of the present invention can be directly or indirectly applied to other related technical fields by making changes and modifications to the embodiments described herein, or by using equivalent structures or equivalent processes performed in the content of the present specification and the attached drawings, which are included in the scope of the present patent.

Claims

1. A circuit board anti-seepage plating method is characterized by comprising the following steps of carrying out alkaline etching after a pattern plating step in the circuit board manufacturing process to expose resin in a base material, and then carrying out alkaline washing, wherein the alkaline washing is to soak the base material in a 3-5% NaOH solution for 3-5 minutes or spray the base material in a 3-5% NaOH solution for 1-2 minutes; then the solder mask step is carried out, and then the gold immersion step is carried out.

2. The method for preventing plating leakage of a circuit board according to claim 1, wherein the circuit board is a board formed by laminating a copper foil and a resin prepreg at a high temperature.

3. The circuit board anti-seepage plating method according to claim 1, wherein the alkaline etching comprises the steps of:

4. The anti-seepage plating method for the circuit board as claimed in claim 1, wherein the method comprises the following steps of cutting, drilling, copper deposition, plate plating, imaging, pattern plating, alkaline etching: stripping, etching, stripping tin, cleaning with 3-5% NaOH, soldering resistance and depositing gold.